For the past one hundred years or so, scientists have been making Carbon/Zinc portable power sources for various applications. In the early days of portable power, these power sources were very large compared to today's standards. For example, the very popular “Igniter Cell” made by Eveready was about 3″ diameter and about 9″ tall and was used in many applications such as radios, buzzers, Xmas lighting, etc. These large cells, as well as some smaller versions, such as the famous Eveready #6 (about 2″ dia.×6″ tall) and the smallest unit cell of the day, the #950 (D size), were commonly made into battery packs with voltages exceeding 40 volts in some applications. These were similar in size, and even larger, than today's car batteries, for uses in lighting devices, radios and car ignition systems. In the mid 1900's, with the advent of advanced electronics such as the transistor, the electrical requirements for portable power sources were drastically reduced. Consequently, cell sizes could also be reduced to include C's, AA's, and AAA's, and even small button cells. This power reduction has continued into the twenty-first century, where applications such as smart labels, smart credit cards, sensors, data loggers, novelty devices such as greeting cards and badges, etc., now require a maximum current of milliamperes, with many applications requiring as little as a few microamperes at about 1.5-3.0 volts. These applications also have the requirement that the power sources be flat and very thin to maintain their low profiles and portability.
In the past twenty-five years, various approaches for making thin, flat cells and batteries were attempted by numerous scientists and corporations. These include the widely known instant film battery pack developed by Polaroid. This battery pack was used in each package of Polaroid instant film. This allowed Polaroid to have a fresh battery in the camera each time the user placed a new pack of film in the camera. This high cost battery with multiple layers and a metal foil laminate package is a high voltage, high current battery, capable of igniting flash bulbs and powering motors, for example, and is not a realistic competitor of the new thin low cost batteries that are needed. In addition to Polaroid, others have tried to develop thin batteries in various electrochemical systems.
In recent years, printed electronics on flexible substrates has become a new process and growing in popularity. In this process, the circuit is printed as well as some of the electronic components. Typically this type of circuit could include a display, IC chip, sensor, antennae, lights and a low capacity power source such as a flat printed battery. In some applications, the power source could also be printed in a totally integrated manner. However, there remain some other applications where economic considerations and/or technical or compatibility considerations make it difficult or non-feasible to print the power source on the circuit. Thus, the power source can be integrated in a different manner. In order to reduce costs, the power source can be a printed as a flat battery that is provided as a complete cell/battery for later integration into the desired circuit. A typical cell can provide about 1.5 volts DC. Where greater voltages are required, it is conventionally known to connect two or more cells in series to increase the voltage. Similarly, multiple cells can be connected together in parallel to increase the effective capacity, as well as increase the current capability. For example, a battery can include two cells electrically connected in series to provide 3 volts DC. Still, it is desirable to reduce the overall size of the battery, even with multiple cells, for use in small circuits.
Co-pending U.S. application Ser. No. 11/110,202 filed on Apr. 20, 2005, Ser. No. 11/379,816 filed on Apr. 24, 2006, Ser. No. 12/809,844 filed on Jun. 21, 2010, Ser. No. 13/075,620 filed on Mar. 30, 2011, and Ser. No. 13/625,366 filed on Sep. 24, 2012, as well as issued U.S. Pat. Nos. 8,029,927, 8,268,475, 8,441,411 are incorporated herein by reference, discuss new designs and methods of manufacture of a flat cell and battery.
With the growing market needs for low cost, low capacity thin flat cells, it would be beneficial to produce a thin, flat, printable flexible cell that is versatile and inexpensive to mass-produce. Printable, disposable thin cells that are well suited for low-power and high-production volume applications would be useful, especially if they offer adequate voltage, sufficient capacity, and low-cost solutions. Conventional low-profile batteries typically have few of these attributes, if any. Still, it is possible to utilize a low-profile battery (i.e., a coin cell or button cell), or any other type of battery, in the instant electrical device.